abstract class Animal {
    public abstract void run();
}
class Dog extends Animal{
    public Dog() {
    }

    @Override
    public void run() {
        System.out.println(1);
    }
}
public class Demo2 {
    final int x = 10;

    public static void main(String[] args) {
        String a = "a"+"b";
    }
    public static void main1(String[] args) {
        String s = "abcde";
        String a = s.concat(s);
        System.out.println(a);
        System.out.println(s.startsWith("a"));
        char[] chars = s.toCharArray();
        StringBuilder stringBuilder = new StringBuilder(s);
        stringBuilder.toString();
    }
}
